Replacing a MOEN bathtub faucet with a Kohler Mistos

My wife and I try to do most of the work in the house myself, so we are a bit handy, and was trying to replace the hardware in the bathtub, however, I'm not sure if I'm overlooking something or I should contract a plumber to do this. I appreciate the time you take to read this and suggestions.
Here's the situation: We moved in to a 1994 house that has one of the universal bathtub (Moen) hardware, and after pulling it off I have the following:

We liked the Kohler "Mistos" set, and purchased it at either Home Depot or Lowe's.
From the Kohler's site (just in the previous line), you can get to the PDF of the instructions on how to install it, but it seems like I need to replace the whole thing that comes from the wall (the cross that is shown in the picture)? Is that correct? Is there any way I can just use the pipes already installed and not have to break wall, etc? I hope I'm just missing something....
I noticed Terry's post on Installing a Kohler Rite-Temp bath & shower valve, K-304 but the instructions are there if you are installing for a brand new house.

Let me know your recommendations. Is it something easy to do? Should I get a Pro to do this instead? or should I just go back to a universal one?

No such thing as a "universal" valve : yours is in fact a moen. There also is absolutely NEVER any possibility of interchangeing parts between brands or models. Your valve is soldered to the pipes.....the most common situation. It will have to be removed to install a new Kohler valve. While not impossible, it is a challenging task to do that working thru that small hole. If there is any way to gain access at the rear, that is easier,

IF you can access the valve from behind this wall, then you won't need to tear up the wall. Otherwise, your choices are: find some new Moen trim that will fit what you have, or, make the hole bigger and install a new valve. Trims are rarely interchangeable between brands, and often even within the same brand. With an old valve, your choices on trim may be very limited.

What a plumber would do is make the hole bigger if it can't be accessed from behind. There are renovation or remodel plates available to cover the larger hole, then the new trim gets installed over that. The shape and finish choices of those varies by brand.

Thanks for the info. Sounds like it will be better to get an updated Moen that fits into the same valve.
From what I can tell on the Moen website is that it is either "Moentrol" or "Posi-Temp" valve, and from looking at them, I think it is a Posi-Temp one. If you happen to know about them, please share.
Otherwise, I'll try to get a faucet that fits to a Posi-Temp valve.